BACTERIAL SEED COMMUNITIES IN SUGAR BEET ARE INFLUENCED BY PROPAGATION SITE AND GENOTYPE

Sugar beet (Beta vulgaris L.) is the most important regional source of sucrose in moderate climates, with Europe and Russia being the core production area worldwide. Recently, an important role of the plant microbiota for resistance breeding was identified. We investigated bacterial seed communities of five different sugar beet cultivars with different degree of tolerance towards Rhizoctonia solani . . , originating from two different propagation sites using 16S rRNA amplicon sequencing, as well as in vitro community change during germination. Bacterial seed communities were dominated by Pseudomonas and Pantoea, together ranging with an abundance between 20-67% of the total seed community. Additional genera, contributing to a variable extent to the seed community, were Paenibacillus (0-25%), Sphingomonas (0.1-17%) and Massilia (0.2-11%) Genotype and propagation site both affected community composition, alpha and beta diversity indices. Different cultivars shared a core community representing 80-91% of the bacterial seed community. Seeds of Rhizoctonia-tolerant cultivars contain a higher relative abundance of the genera Paenibacillus, Kosakonia, and Enterobacter. The majority of seed endophytes (63-83%) survives the process of germination, representing dominant taxa of seeds but with a community shift towards Enterobacteriaceae. Bacterial alpha diversity is higher in seeds than in seedling roots, indicating vacant niches in the young seedling for substrate-derived microorganisms. Our results demonstrate the compositional plasticity of bacterial seed microbiomes using sugar beet as a model plant, highlighting